阅读说明：本技术 一种以钙盐法生产乳酸的发酵液为原料生产α-半水硫酸钙晶须并同步回收乳酸单体的方法 (Method for producing alpha-calcium sulfate hemihydrate crystal whisker by taking fermentation liquor for producing lactic acid by calcium salt method as raw material and synchronously recovering lacti) 是由 王正祥 牛丹丹 田康明 路福平 申春莉 于 2020-12-31 设计创作，主要内容包括：本发明公开了一种以钙盐法生产乳酸的发酵液为原料生产α-半水硫酸钙晶须并同步回收乳酸单体的方法。包括如下步骤：1)乳酸发酵结束后,将发酵液升温；2)打开搅拌,加入硫酸反应；3)反应结束后,过滤收集固体部分即为α-半水硫酸钙晶须,收集液体部分即为含乳酸单体的游离乳酸液；4)获得的α-半水硫酸钙晶须再经过洗涤干燥后即为α-半水硫酸钙晶须成品,获得的游离乳酸液经过过滤、浓缩,即为乳酸粗成品,经过精制,获得高纯度乳酸单体。本发明可替代现有钙盐法乳酸生产中的乳酸高效分离和硫酸钙副产物的高附加值转化,显著降低乳酸精制成本和废弃物的形成,有利于乳酸生产质量提升和后提取工艺技术简化。(The invention discloses a method for producing alpha-calcium sulfate hemihydrate crystal whiskers by taking fermentation liquor produced by lactic acid by a calcium salt method as a raw material and synchronously recovering lactic acid monomers. The method comprises the following steps: 1) after the lactic acid fermentation is finished, heating the fermentation liquor; 2) opening the stirrer, and adding sulfuric acid for reaction; 3) after the reaction is finished, filtering and collecting a solid part, namely the alpha-calcium sulfate hemihydrate crystal whisker, and collecting a liquid part, namely free lactic acid liquid containing lactic acid monomers; 4) and washing and drying the obtained alpha-calcium sulfate hemihydrate crystal whisker to obtain an alpha-calcium sulfate hemihydrate crystal whisker finished product, filtering and concentrating the obtained free lactic acid solution to obtain a crude lactic acid product, and refining to obtain a high-purity lactic acid monomer. The method can replace the high-efficiency separation of lactic acid and the high value-added conversion of calcium sulfate byproducts in the existing calcium salt method lactic acid production, remarkably reduce the refining cost of lactic acid and the formation of wastes, and is favorable for improving the production quality of lactic acid and simplifying the post-extraction process technology.)

1. A method for producing alpha-calcium sulfate hemihydrate crystal whiskers by taking fermentation liquor for producing lactic acid by a calcium salt method as a raw material and synchronously recovering lactic acid monomers is characterized by comprising the following steps:

step 1: after the lactic acid fermentation is finished, heating the fermentation liquor;

step 2: opening the stirrer, maintaining the temperature, adding sulfuric acid, and reacting;

and step 3: after the reaction is finished, carrying out solid-liquid separation on the reaction liquid through filtration, collecting a solid part, namely the alpha-calcium sulfate hemihydrate crystal whisker, and collecting a liquid part, namely free lactic acid liquid containing a lactic acid monomer;

step 4-1: washing and drying the obtained alpha-calcium sulfate hemihydrate crystal whisker to obtain a finished product of the alpha-calcium sulfate hemihydrate crystal whisker;

step 4-2: the obtained free lactic acid solution is filtered and concentrated to obtain a lactic acid crude product, and the lactic acid crude product is refined to obtain the high-purity lactic acid monomer.

2. The method of claim 1, wherein the temperature is raised in situ after the lactic acid fermentation in step 1 is completed or moved to a post-extraction reactor.

3. The method of claim 1, wherein the temperature of the fermentation broth in step 1 is raised to a temperature of 50 ℃ to 102 ℃.

4. The method of claim 3, wherein the temperature of the fermentation broth in step 1 is raised to a temperature of 85 ℃ to 102 ℃.

5. The method of claim 1, wherein the reaction of step 2 is maintained at a stirring speed of 5 to 80 r/min.

6. The method according to claim 1, wherein the concentration of the sulfuric acid added in the step 2 is 2 mol/L-12 mol/L, and the total amount of the sulfuric acid is controlled in a molar ratio of the lactic acid to the sulfuric acid of 1: 0.499-1: 0.501, controlling the time limit of adding the total amount of sulfuric acid to be 1 min-2 h/ton of fermentation liquor, and maintaining the reaction for 1 min-10 h after all the sulfuric acid is added.

7. The method according to claim 1, characterized in that the solid-liquid separation of step 3 is performed with a belt filter device having a pore size of 5.0 μm to 50 μm.

8. The method according to claim 1, wherein the alpha-calcium sulfate hemihydrate whiskers obtained in the step 4-1 are washed with hot water or absolute ethanol, and then flash-dried by steam at 101-160 ℃ to obtain finished alpha-calcium sulfate hemihydrate whiskers.

9. The method according to claim 1, characterized in that the free lactic acid solution obtained in the step 4-2 is filtered and decontaminated through a plate frame with a filtering aperture of 0.8-10 μm, and then is evaporated and concentrated to a lactic acid content of 20-60 wt%, so that a crude lactic acid product is obtained.

Technical Field

The invention belongs to the field of fermentation engineering and chemical engineering, and particularly relates to a method for directly converting calcium lactate fermentation liquor into alpha-calcium sulfate hemihydrate whiskers and free lactic acid under the action of sulfuric acid during lactic acid fermentation production.

Background

Lactic acid is an important three-carbon organic acid with two optical configurations, L-and D-forms, namely: l-lactic acid and D-lactic acid. L-lactic acid and D-lactic acid are monomer raw materials for synthesizing polylactic acid and are important components of biodegradable materials. In addition, L-lactic acid and D-lactic acid are also used as raw materials for synthesizing various esters (such as methyl lactate, ethyl lactate, propyl lactate and butyl lactate) and lactate, L-lactic acid is also widely used as an acidifier in the production of products such as food, beverage, condiment, wine and feed, and D-lactic acid is also used as a raw material for synthesizing essences, spices, herbicides, medicaments and the like.

The mode of production of lactic acid is mainly carried out by microbial fermentation, wherein the calcium salt method is the most important method for producing lactic acid by fermentation. Namely: a carbon source (such as glucose, glycerol, xylose, lactose, sucrose, fructose) suitable for the metabolism of Microbial strains is D-lactic acid or L-lactic acid (Tian, et. al, Biotechnology Bioengineering, 2016, 113: 181-, after the fermentation is finished, the formed calcium lactate is converted into free lactic acid by adding sulfuric acid, and calcium sulfate which is insoluble in water is generated and is separated out of the solution in the form of amorphous dihydrate. The fermentation liquor containing free lactic acid is refined by lactic acid through a series of procedures of separation and purification and the like to produce lactic acid products, the formed calcium sulfate insoluble in water is a byproduct (Zhangpeng et al, ZL 200810049644.4) produced by lactic acid fermentation, and the calcium sulfate dihydrate, namely gypsum, is produced through procedures of separation, drying and the like.

In the process of producing lactic acid by calcium salt fermentation, the generation amount of calcium sulfate dihydrate (gypsum) is large, and the quality of the calcium sulfate dihydrate is equivalent to the amount of lactic acid products. Because of the general physicochemical properties of the dihydrate calcium sulfate (gypsum), most of the dihydrate calcium sulfate is currently applied to the preparation of food-grade gypsum, low-end cement additives, feed additives and the like, has low application value and even becomes solid waste, and is extremely unfavorable for large-scale lactic acid production (Zhang et al, inorganic salt industry, 2017, 49 (8): 10-13).

The method is an important way for solving the large-scale production of lactic acid by a calcium salt method, and can solve the problem of generation of calcium sulfate dihydrate (gypsum) by-products while ensuring the large-scale industrial production of the lactic acid.

In the prior art, beta-type semi-hydrated gypsum (CaSO) can be obtained by calcining and grinding gypsum₄·0.5H₂O), namely building gypsum, also called plaster and plaster. The calcining temperature is increased to 190 ℃, so that the model gypsum can be obtained, and the fineness and the whiteness of the model gypsum are higher than those of the building gypsum; when the calcining temperature is increased to 400-500 ℃ or more than 800 ℃, the gypsum can be converted into floor gypsum, the gypsum is slow to set and harden, but the strength, the wear resistance and the water resistance after hardening are better than those of common building gypsum (Zhang Qian, etc., green environment-friendly building materials 2020, (02): 14-15, 18). However, the physical calcination scheme for converting gypsum into beta-hemihydrate or sewage gypsum is not suitable for the processing of calcium sulfate byproduct in lactic acid fermentation production, mainly because of the dihydrate generated in the lactic acid fermentation production processThe absolute amount of calcium sulfate is relatively small, the added value of the product is not high, and the investment-benefit is limited.

In recent years, a brand-new method is established in many researches, and gypsum can be converted into alpha-calcium sulfate hemihydrate whiskers (poplar, et al, ZL201910466020.0; Stepeyang, et al, ZL 201910373883.3; Wang Hongyu, et al, ZL201610547294.9; Zhoufeng, et al, silicate report, 2017, 36: 2090-. The alpha-calcium sulfate hemihydrate crystal whisker has high strength, high modulus, high toughness, high insulativity, wear resistance, high temperature resistance, acid and alkali resistance, good infrared reflectivity, easy surface treatment, easy compounding with polymer, no toxicity and other excellent physical and chemical properties, and has very high application value (Liming, fine and special chemicals 2016, 24(6): 47-50), and may be used as reinforcing toughening agent or functional filler (Naway, etc. in resin, plastic, rubber, paint, paper, asphalt, friction and sealing material, 2014:1671-, the academy of Sichuan institute of technology (Nature science edition), 2013, 26(5): 7-10; lvceng et al, chemical evolution, 2013, 32: 842-sand 847, 890; wangzhouhong, etc., mining and metallurgy, 2005(2): 38-41); it can also be directly used as filter material, heat insulating material, fire-resistant heat-insulating material, infrared reflecting material and high-insulating material for covering electric wire (Huangmingjie et al, fire-resistant and lime 2014, 39(3): 19-20, 23; Huangmingjie et al, modern paint and coating 2013, 16(11): 18-19, 26).

The reported methods for converting gypsum into alpha-calcium sulfate hemihydrate whiskers mainly comprise the following methods:

(1) steam pressing method: crushing natural calcium sulfate dihydrate into a block material with the thickness of 20-50 mm, putting the block material into an autoclave by using a metal frame or a trolley, and carrying out split type and horizontal type steaming and pressing methods. Introducing steam condensate water or hot flue gas to heat the materials to 50-70 ℃, discharging the condensate water or the hot flue gas, sealing the autoclave, then introducing saturated steam, heating to 120-160 ℃, keeping the pressure, carrying out autoclave dehydration and crystal transformation for 5-8 h to convert the materials into alpha-calcium sulfate hemihydrate whiskers, and then removing the alpha-calcium sulfate hemihydrate whiskers from the autoclave for drying or drying the alpha-calcium sulfate hemihydrate whiskers in the autoclave. The production period of the vertical still kettle is about 16-18 h, and the production period of the horizontal still kettle is about 30-40 h (Gunn Qing Yu et al, artificial crystal bulletin, 2016, 45: 1892-. The method is a traditional process, the process is simple, the production period is long, the production cost is high, the product quality fluctuation is large, the product strength is low due to uneven heating of the blocky raw materials and uneven dehydration, crystal transformation and drying, and the general strength is about 20-30 MPa.

(2) Hydrothermal method: grinding natural calcium sulfate dihydrate into fine powder, adding the fine powder into an aqueous solution containing a crystal transformation promoter to prepare a suspension with a solid content not more than 30%, adding the suspension into a vertical autoclave, continuously stirring the suspension, simultaneously heating the suspension, evaporating water to form steam, generating pressure to form an autoclave condition, reacting for about 0.5-8 h under the autoclave condition of 120-180 ℃, completing dehydration and crystal transformation processes, exhausting and reducing pressure, and performing centrifugal dehydration, washing, drying and grinding to obtain a finished product. After crushing and grinding, mixing with water to prepare slurry, adding some additives capable of promoting crystallization conversion or named as crystal transformation agents, then adding the slurry into an autoclave with a steam jacket, stirring while introducing steam into the jacket for heating, and converting the dihydrate gypsum into alpha-calcium sulfate hemihydrate crystal whiskers with good crystallization. Then exhausting steam and reducing pressure, discharging slurry, dehydrating, washing, drying and grinding to obtain the alpha-type high-strength gypsum powder. The alpha-calcium sulfate hemihydrate produced by the method has stable product quality and high compressive strength, and can reach 40-80 MPa (Tangna and other inorganic salt industries 2020, 52(4): 88-92; Wufeng and other chemical engineering progresses 2018, 37: 1536-. However, the method has the disadvantages of complex process, more production equipment, large investment, small production capacity, low production efficiency and high production cost, and cannot be directly integrated into the lactic acid fermentation production process.

(3) Normal pressure salt solution method: and mixing the finely ground calcium sulfate dihydrate with a salt solution added with a crystal modifier, adding the mixture into a reaction vessel, and boiling the mixture under normal pressure to convert the calcium sulfate dihydrate into the alpha-calcium sulfate hemihydrate crystal whiskers. Then the alpha-calcium sulfate hemihydrate crystal whisker is prepared by dehydration, washing and drying. The method does not need a pressure container, and can reduce equipment investment (Wang ai wen and the like, nonmetallic minerals, 2020, 43(4): 84-87; Zhang Huiyong, chemical minerals and processing, 2020, 49(1): 50-54; Pawenjian and the like, university of east China science and technology (natural science edition), 2019, 45(2): 266-. But the process conditions are strict, the reaction time is longer, and the product strength is not high. At present, the method is still in a laboratory test stage, and no industrial production example is seen.

(4) The normal pressure glycerol method comprises the following steps: adding industrial byproduct calcium sulfate dihydrate into 45-75% of glycerol solution, adding a certain amount of crystal form regulator, maintaining at 90 ℃ for 30 min, filtering, washing and drying to obtain the alpha calcium sulfate hemihydrate crystal whisker. The method does not need high pressure environment, and has mild reaction condition and high product purity. However, the prepared alpha-type calcium sulfate hemihydrate crystal whisker has low length and small hardness (Tuqingjun et al, mineral protection and utilization, 2019, 39(4): 1-8). At present, the method is in a laboratory test stage, and no production example is seen.

The method for preparing the alpha-calcium sulfate hemihydrate crystal whisker takes calcium sulfate dihydrate as a starting material, most of the production processes need to be carried out at a temperature higher than 120 ℃, and different compounds need to be added in part of the methods, so that the manufacturing cost is increased, and the generation of byproducts is increased. It can be seen that the existing production technology of alpha-calcium sulfate hemihydrate whisker can not directly prepare the alpha-calcium sulfate hemihydrate whisker while preparing the lactic acid monomer from the lactic acid fermentation broth of the calcium salt method. In addition, excessively high reaction temperature and addition of a crystal modifier may significantly affect recovery of lactic acid monomer.

So far, the release process of lactic acid in calcium lactate generated in the process of producing lactic acid by a calcium salt method is based on the formation of calcium sulfate by-products, the synchronous formation of lactic acid release and the preparation of alpha-calcium sulfate hemihydrate crystal whisker cannot be realized, calcium sulfate solid waste needs to be further treated in the subsequent production, the production cost is increased, and the production process is not green and environment-friendly enough. Therefore, the synchronous production of the lactic acid monomer and the alpha-calcium sulfate hemihydrate crystal whisker is realized, on one hand, the production process of the lactic acid can be intensified and the production investment of the lactic acid is reduced, and on the other hand, the formation of the calcium sulfate waste in the existing industrial production system can be thoroughly solved. Therefore, the economic efficiency and the environmental benefit of the lactic acid fermentation production can be obviously improved, the comprehensive cost of the lactic acid production can be obviously reduced, and the method has important significance for promoting the technical progress of the lactic acid fermentation industry and the healthy development of the polylactic acid industry chain.

Disclosure of Invention

The invention aims to directly release free lactic acid from calcium lactate fermentation liquor in the production of lactic acid by calcium salt fermentation, and simultaneously generate the replaced calcium sulfate in an alpha-calcium sulfate hemihydrate whisker mode, thereby realizing the synchronous production of lactic acid monomers and the alpha-calcium sulfate hemihydrate whisker.

In order to achieve the purpose, the technical scheme provided by the invention comprises the following steps:

a method for producing alpha-calcium sulfate hemihydrate crystal whisker and synchronously recovering lactic acid monomer by taking fermentation liquor for producing lactic acid by a calcium salt method as a raw material comprises the following steps:

step 1: after the lactic acid fermentation is finished, heating to 50-102 ℃ on site or transferring the fermentation liquor into a post-extraction reaction kettle; further, the temperature of the fermentation broth is raised to not less than 50 ℃ but not more than 102 ℃, further not less than 55 ℃ but not more than 102 ℃, not less than 60 ℃ but not more than 102 ℃, not less than 65 ℃ but not more than 102 ℃, not less than 70 ℃ but not more than 102 ℃, not less than 75 ℃ but not more than 102 ℃, not less than 80 ℃ but not more than 102 ℃, not less than 85 ℃ but not more than 102 ℃;

step 2: opening stirring, adding 2-12 mol/L sulfuric acid while maintaining the temperature, and maintaining the reaction for 1 min-10 h; further, the reaction is carried out under stirring at 5-80 r/min and temperature maintenance, and the total amount of the added sulfuric acid is controlled in a manner that the molar ratio of the lactic acid to the sulfuric acid is 1: 0.499-1: 0.501, controlling the time limit of adding the total amount of sulfuric acid to be 1 min-2 h/ton of fermentation liquor, and maintaining the reaction for 1 min-10 h after all the sulfuric acid is added;

and step 3: after the reaction in the step 2 is finished, carrying out solid-liquid separation on the reaction liquid through filtration, collecting a solid part, namely the alpha-calcium sulfate hemihydrate crystal whisker, and collecting a liquid part, namely free lactic acid liquid containing a lactic acid monomer; further, the described solid-liquid separation is carried out by adopting a belt type filtering device with the aperture of 5.0-50 mu m;

step 4-1: washing and drying the obtained alpha-calcium sulfate hemihydrate crystal whisker to obtain a finished product of the alpha-calcium sulfate hemihydrate crystal whisker; further, washing the alpha-calcium sulfate hemihydrate crystal whisker by hot water or absolute ethyl alcohol, and then carrying out flash evaporation drying by steam at the temperature of 101-160 ℃ to obtain a finished product of the alpha-calcium sulfate hemihydrate crystal whisker;

step 4-2: filtering and concentrating the obtained free lactic acid solution to obtain a crude lactic acid product, which can be used for subsequent refining such as nanofiltration, decolorization, ion exchange and the like to obtain a high-purity lactic acid monomer; further, filtering the obtained free lactic acid solution through a plate frame with the filtering aperture of 0.8 to 10 mu m to remove impurities, and then evaporating and concentrating the free lactic acid solution to reach the lactic acid content of 20 to 60wt%, thus obtaining a crude lactic acid product.

According to the method, the recovery rate of the lactic acid monomer reaches over 99.5 percent, and the recovery rate of calcium sulfate and the generation rate of the alpha-calcium sulfate hemihydrate crystal whisker reach over 98 percent.

Has the advantages that:

the invention can convert the lactate liquid by the calcium salt method into free lactate liquid and alpha-calcium sulfate hemihydrate crystal whiskers by one step, realizes the synchronous production of the lactic acid monomer and the alpha-calcium sulfate hemihydrate crystal whiskers, has the recovery rate of the lactic acid monomer reaching more than 99.5 percent, and has the recovery rate of calcium sulfate and the generation rate of the alpha-calcium sulfate hemihydrate crystal whiskers reaching more than 98 percent, thereby being capable of intensifying the production process of lactic acid and reducing the production investment of lactic acid on one hand, and being capable of thoroughly solving the formation of calcium sulfate waste in the existing industrial production system on the other hand. Therefore, the economic efficiency and the environmental benefit of the lactic acid fermentation production can be obviously improved, and the comprehensive cost of the lactic acid production can be obviously reduced. The invention can be applied to the generation of other organic acids such as citric acid, malic acid, succinic acid and the like after simple modification.

When the invention is used for converting lactic acid in calcium lactate by using sulfuric acid, the invention discovers that the amorphous calcium sulfate dihydrate originally generated in the process can be converted into alpha-calcium sulfate hemihydrate crystal whiskers by only giving a certain temperature, not influencing the subsequent separation and refining of the lactic acid and controlling the adding speed of the sulfuric acid. The key points of the process are the temperature and the sulfuric acid addition speed, wherein the temperature cannot be too high as that of the existing document, the temperature exceeds 105 ℃, the loss of lactic acid is large, and the lactic acid is a main product; it is also not possible to add any trans-or pro-crystallizers because that would increase the cost of the lactic acid isolation purification.

Drawings

Fig. 1 is a route of lactic acid production process: (a) the original production process; (b) the process of the invention;

figure 2 is a map (100X) of the morphology of alpha-calcium sulfate hemihydrate whiskers.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present patent and are not intended to limit the present invention.

The method comprises the steps of taking a fermentation liquid for producing lactic acid by a calcium salt method as a raw material, heating the fermentation liquid to 50-102 ℃ after fermentation of the lactic acid is finished, adding 2-12 mol/L sulfuric acid, maintaining the reaction for 1 min-10 h, carrying out solid-liquid separation by filtering, collecting a solid part which is alpha-calcium sulfate hemihydrate crystal whisker, collecting a liquid part which is free lactic acid liquid containing a lactic acid monomer, washing and drying the obtained alpha-calcium sulfate hemihydrate crystal whisker to obtain an alpha-calcium sulfate hemihydrate crystal whisker finished product, filtering and concentrating the obtained free lactic acid liquid to obtain a crude lactic acid product, and obtaining the high-purity lactic acid monomer by subsequent refining such as nanofiltration, decolorization, ion exchange and the like (figure 1).

The main experimental method adopted by the invention is as follows:

1. preparation of lactic acid fermentation liquor by calcium salt method

The preparation of the lactic acid fermentation liquor by the calcium salt method is carried out according to the method of the invention granted by the patent at the earlier stage (Wangzhenxiang, etc., ZL 201580000781.7), the fermentation strain is CGMCC 11059 or CGMCC11060, wherein the strain CGMCC 11059 is used for the fermentation production of D-lactic acid, and the strain CGMCC11060 is used for the fermentation production of L-lactic acid (Wangzhenxiang, etc., ZL 201580000781.7). In the initial stage of fermentation, adding glucose into a fermentation minimal medium to a final concentration of 10-50 g/L, and culturing at 30-37 ℃, at a pH of 5.5-7.5, under the condition of ventilation of 0.1-2.0 vvm and stirring of 100-1000 r/min; the culture time is 5-15 h, and the bacterial mass reaches 10-50 OD; closing ventilation, reducing the stirring speed to 0-300 r/min, increasing the fermentation temperature to 37-50 ℃, supplementing a glucose solution with the final concentration of 16-25%, controlling the feeding speed to be 3 g/(L h) -25 g/(L h), synchronously feeding 5-35% of calcium hydroxide, and controlling the fermentation pH to be 5.0-8.0.

2. Acidification of fermentation liquor and preparation of calcium sulfate alpha-type crystal whisker

After fermentation is finished, heating the fermentation liquor to 50-102 ℃, starting stirring, adding 2-12 mol/L sulfuric acid while maintaining the temperature, wherein the total amount of the sulfuric acid is controlled in a molar ratio of lactic acid to sulfuric acid of 1: 0.499-1: 0.501, controlling the speed of adding the total amount of sulfuric acid to be 1 min-2 h/ton of fermentation liquor, and maintaining the reaction for 1 min-10 h.

3. Separation of lactic acid liquid and alpha-calcium sulfate hemihydrate crystal whisker

After the reaction is finished, solid-liquid separation is carried out on the reaction liquid through filtration, a belt type filtering device with the aperture of 5.0 mu m-50 mu m is adopted for carrying out the solid-liquid separation, the collected solid part is alpha-calcium sulfate hemihydrate crystal whiskers, and the collected liquid part is free lactic acid liquid containing lactic acid monomers.

4. Refining of alpha-calcium sulfate hemihydrate crystal whisker

And washing and drying the obtained alpha-calcium sulfate hemihydrate crystal whisker, washing with hot water or absolute ethyl alcohol, and performing flash evaporation drying at the temperature of 101-160 ℃ by using steam to obtain the alpha-calcium sulfate hemihydrate crystal whisker finished product.

5. Analysis of alpha-calcium sulfate hemihydrate whisker morphology

The appearance of the whiskers was observed and recorded under an optical microscope. The length and diameter of 40 whiskers were measured and their aspect ratio was calculated. All data are the average of the results of 3 replicates.

6. Yield of alpha-calcium sulfate hemihydrate crystal whisker

The yield of the alpha-calcium sulfate hemihydrate crystal whisker can be expressed as the ratio of the actual value to the theoretical value of the crystal whisker. The actual value is the quality of the finished product of the alpha-calcium sulfate hemihydrate crystal whisker. The theoretical value is the weight of the alpha-calcium sulfate hemihydrate crystal whisker obtained by calculating according to the mole number of the added sulfuric acid during acidification. The mole number of the sulfuric acid is equal to that of the alpha-calcium sulfate hemihydrate crystal whisker, and the product of the mole number of the sulfuric acid and the relative molecular mass of the alpha-calcium sulfate hemihydrate crystal whisker is the theoretical value of the crystal whisker and is counted by percent.

7. Lactic acid content, quality and yield

D-lactic acid, L-lactic acid, pyruvic acid, formic acid, acetic acid and succinic acid content determination: HPLC is adopted, and the chromatographic detection conditions are as follows: the chromatographic column is an HPX-87H organic acid analytical column, the column temperature is 65 ℃, the detection wavelength is 210 nm, the mobile phase is a sulfuric acid solution with the concentration of 5 mmol/L, the flow rate is 0.8 mL/min, and the sample injection amount is 10 mu L. All data are the average of the results of 3 replicates. The content of the lactic acid monomer is in g/L, and the chemical purity of the lactic acid is in percent (%) of the lactic acid monomer to the total organic acids. The sugar-acid conversion of lactic acid was calculated as the percentage (%) of the total lactic acid production mass to the total glucose consumption.

And (3) measuring the optical purity of the lactic acid monomer: HPLC is adopted, and the chromatographic detection conditions are as follows: the chromatographic column is an Astec CLC-L optical purity analytical column, the column temperature is 25 ℃, the detection wavelength is 254 nm, the mobile phase is a copper sulfate solution with the concentration of 5 mmol/L, the flow rate is 1 mL/min, and the sample injection amount is 10 mu L. All data are the average of the results of 3 replicates. The optical purity of the lactic acid monomer is calculated as the mass percent (%) of L-lactic acid or D-lactic acid to the total lactic acid.

Calculating the calcium lactate concentration: the free lactic acid content is converted to calcium lactate content in terms of molar ratio, i.e. 1 mole of calcium lactate is formed by 2 moles of free lactic acid combined with a calcium salt.

Example 1: preparation of lactic acid fermentation broth

Inoculating frozen glycerol tube of D-lactic acid production strain CGMCC 11059 or L-lactic acid production strain CGMCC11060 into 50 mL LB liquid culture medium at 37 deg.C,Shaking-culturing at 200 r/min for 12 h to obtain first-stage seed liquid. Inoculating the first-stage seed solution into 150 mL of M9 liquid culture medium with glucose as carbon source, wherein the initial sugar concentration is 0.5%, and shake culturing is carried out at 37 ℃ and 200 r/min for 10 h to obtain the second-stage seed solution. Inoculating the second-stage seed solution into a fermentation tank containing M9 liquid culture medium according to the inoculation amount of the initial OD value of 0.3, wherein the initial volume of the fermentation tank after inoculation is 25L, the addition amount of the initial invert syrup is 3%, and the fermentation production of the lactic acid monomer is started. The initial fermentation temperature is controlled at 37 deg.C, pH is maintained at 6.5 with ammonia water, aeration amount is adjusted to 1.5 vvm during thallus growth, stirring speed is 1000 r/min, and when thallus concentration reaches OD₆₀₀And after 30, closing ventilation, controlling the fermentation temperature at 40 ℃, adjusting the stirring rotation speed to 200 r/min, feeding 25% calcium hydroxide suspension to maintain the pH at 7.0, supplementing total 6.0 kg of glucose, and ending fermentation after the concentration of residual sugar is lower than 0.5 g/L. The key fermentation results are summarized in table 1.

TABLE 1 lactic acid monomer fermentation broth preparation and its main parameters

Example 2: preparation of alpha-calcium sulfate hemihydrate crystal whisker

The lactic acid fermentation broth obtained in the above example 1 was heated to 88 ℃ in a reaction kettle and maintained at this temperature, 5 mol/L sulfuric acid solution was added under stirring at 20 r/min, the total amount of sulfuric acid was controlled to be a molar ratio of lactic acid to sulfuric acid of 1:0.5, and the time limit for the addition of the total sulfuric acid solution was controlled to be 1 hour/ton of fermentation broth; after all the sulfuric acid solution is added, the reaction is maintained for 15 min; after the reaction is finished, solid-liquid separation of reaction liquid is carried out by adopting a belt type filtering device with the aperture of 8.0 mu m, the collected solid part is alpha-calcium sulfate hemihydrate crystal whisker, and the obtained alpha-calcium sulfate hemihydrate crystal whisker is washed by absolute ethyl alcohol and is subjected to flash evaporation drying at 120 ℃ to obtain a finished product of the alpha-calcium sulfate hemihydrate crystal whisker; collecting the liquid part, namely free lactic acid liquid containing lactic acid monomers, filtering and removing impurities through a plate frame with the filtering aperture of 6 mu m, evaporating and concentrating to obtain a crude lactic acid product with the lactic acid content of 20-60 wt%, and performing refining processes such as ion exchange, activated carbon decoloration and ultrafiltration to obtain the high-purity lactic acid monomers. According to the method, the generation rate of the alpha-calcium sulfate hemihydrate whiskers reaches more than 98 percent (table 2), the calcium sulfate whiskers are alpha-type, the length-diameter ratio of the whiskers is 13.2-130.2, the length-diameter ratio of 80 percent of the whiskers is 54.3-85.0 (table 3), and the recovery rate of the lactic acid monomer reaches more than 99.5 percent (table 4).

TABLE 2 formation rate of alpha-calcium sulfate hemihydrate whiskers

TABLE 3 aspect ratio of alpha-calcium sulfate hemihydrate whiskers

TABLE 4 recovery of lactic acid monomer

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.